What lens/es for holiday with a family

Another vote for just the 15-85mm IS. If you're on vacation then you just want to enjoy the vacation. The 15-85mm IS is a very capable lens and you avoid any lens changes and time lost in deciding what to use.

My usual vacation "kit" is a 50D, 10-22mm EF-S, 15-85mm IS EF-S, Tamron 60mm F2.0 Macro (low-light and portraits as well) and 55-250mm EF-S. I have a Kata backpack that holds all these plus the usual extras (580 EX Flash, spare batteries, spare CF cards etc.). However, I almost always just use the 15-85mm IS. It's only if I have the time and inclination to do some "photography" that any of the other lenses come out.